On 5/30/06 at 5:48 AM, actuary at mchsi.com wrote:
>While a Mathematica user for some time, use has been limited to
>number crunching and not symbolic manipulations. I started to
>remedy this over the weekend.
>I entered Sum[x[i],{i,1,50}] expecting to see a response with
>Summation sign. Instead the output was x[1}+x[2]+x[3]+.....
>What do I need to do to get output that includes the Summation sign?
>StandardForm was checked.
By default, Mathematica attempts to evaluate any input. So, when you give definite limits for the Sum, the output is what you have seen. To get an output with the summation sign, you could use Hold to prevent evaluation of the summand, e.g.,
Hold[Sum[x[i], {i, 1, 50}]] // TraditionalForm
Alternatively, you could replace the upper limit with a variable, e.g.,
s = Sum[x[i], {i, 1, n}] // TraditionalForm
This second form tends to be more useful since you can use a replacement rule later to set the value of n, e.g.,
s/.n->50
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